LJ::may_lock — see if we COULD get a mysql lock on a given key/dbrole combination, but don't actually get it.
LJ::may_lock(db, dbrole);
db.
dbrole. the role this lock should be gotten on, either 'global' or 'user'
cgi-bin/ljlib.pl
undef if called improperly, true on success, die() on failure